1. Technical Field of the Invention
This invention relates generally to wireless communication systems and more particularly to interoperability within a wireless communication system between next generation and legacy wireless terminals.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices; Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11 (Wireless Local Area Networks “WLANs), Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
As is also known, the receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies then. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
As is further known, the data recovery stage performs numerous operations to recover data from the filtered signals. Such operations include, for an IEEE 802.11a or IEEE 802.11g compliant receiver, guard interval removal, fast Fourier transform, de-mapping and slicing, de-interleaving, and decoding. The decoding utilizes a channel estimation to produce the recovered data from de-interleaved data. In accordance with the IEEE 802.11a and/or IEEE 802.11g standard, a frame includes a short training sequence (STS), a long training sequence (LTS), a signal field, and a plurality of data fields. The IEEE 802.11a and/or IEEE 802.11g standard further indicates that channel estimation is to be done during the long training sequence. Once the channel estimation is determined, it is used for the remainder of the frame.
Currently, next generation WLANs are being developed that will co-exist with IEEE 802.11a, IEEE 802.11b, and/or IEEE 802.11g stations (STAs) and access points (APs). One contemplated next generation system includes a Multi-Input-Multi-Output (MIMO) interface (802.11n). The MIMO interface of the next generation system must be interoperable with the legacy STAs and base stations. Interoperability requires that the legacy devices identify next generation transmissions and respond accordingly. Such interoperation includes at least two particular operations. In a first operation, an AP supports both legacy and next generation STAs. In a second operation, legacy and next generation STAs share a channel, i.e., co-channel/“overlapping” BSS. In each of these cases the Physical Layer Convergence Procedure (PLCP) header must allow an IEEE 802.11a/b/g STA to identify next generation transmissions and to deassert clear channel assessment (CCA) indication or use a protection mechanism like Request-to-Send/Clear-to-Send (RTS/CTS) or CTS-to-sent procedures to avoid conflict with the transmissions. In each of these cases, the next generation preamble must be backwards compatible in order to allow the legacy devices to recognize the next generation transmissions.
Next generation devices are required to meet particular data throughput requirements. One such requirement is that an effective data rate should meet or exceed 100 Mbps. This requirement translates to a 130 Mbps requirement at the PHY of the devices. Of course, this higher data rate is satisfied as a tradeoff in reach because transmit power is limited. In meeting these requirements, the characteristics of the transmitter and receiver must be selected. Therefore, a need exists for a next generation that meets these requirements.